In elevators it is common to use one or more automatic sliding doors. Systems are used to detect the presence of an obstruction between the doors before and during closure for the protection of the passengers. Typically the systems, in the event of an obstruction, prevent the elevator doors from closing further and, preferably, reopen them.
One known system for detecting objects in the path of elevator doors places a light beam in a path across the door opening and uses a sensor to detect an interruption of the light beam, which would occur if an obstruction is between the door. Upon sensing the interruption, the sensor issues a signal to alter the control of the door operation, and preferably reopen the doors.
The system has an array of light sources disposed vertically on one side of the door, producing light beams, and a corresponding array of photosensitive detectors arranged on the other door, for sensing those light beams, thus creating a system which can sense objects at different heights in the doorway.
This system, although generally satisfactory, has the disadvantage of only having the ability to detect objects which penetrate in or about the mid-plane of the doorway. For example, objects such as fingers on the edge of the door, which are in the volume swept by the closing doors but do not extend into the light path, will go undetected. This depth detection problem could be improved, for instance, by mounting emitters and detectors on both edges of the doors. However, the additional emitters and detectors, disposed to the elevator car doors and/or disposed to the hoistway doors, would significantly add to the cost and the complexity of the detection system.